Annealed and promoted catalyst

ABSTRACT

A mixed metal oxide, which may be an orthorhombic phase material, is improved as a catalyst for the production of unsaturated carboxylic acids, or unsaturated nitriles, from alkanes, or mixtures of alkanes and alkenes, by: contacting with a liquid contact member selected from the group consisting of organic acids, alcohols, inorganic acids and hydrogen peroxide to form a contact mixture; recovering insoluble material from the contact mixture; calcining the recovered insoluble material in a non-oxidizing atmosphere; admixing the calcined recovered insoluble material with (i) at least one promoter element or compound thereof and (ii) at least one solvent for the at least one promoter element or compound thereof; removing the at least one solvent to form a catalyst precursor; and calcining the catalyst precursor.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional application is a divisional of non-provisional U.S.patent application Ser. No. 10/117,904, filed Apr. 8, 2002, now U.S.Pat. No. 6,645,905, benefit of which is claimed under 35 U.S.C. § 120and which in turn claims benefit under 35 U.S.C. § 119(e) of U.S.provisional Application No. 60/286,278, filed Apr. 25, 2001, prioritybenefit of which is also claimed for the present divisional application.

The present invention relates to a catalyst for the oxidation ofalkanes, or a mixture of alkanes and alkenes, to their correspondingunsaturated carboxylic acids by vapor phase catalytic oxidation and,more particularly, to a method of making the catalyst and to a processfor the vapor phase catalytic oxidation of alkanes, or a mixture ofalkanes and alkenes, to their corresponding unsaturated carboxylic acidsusing a catalyst prepared by the present method of making a catalyst.The present invention also relates to a process for the vapor phasecatalytic oxidation of alkanes, or a mixture of alkanes and alkenes, inthe presence of ammonia, to their corresponding unsaturated nitritesusing a catalyst prepared by the present method of making a catalyst.

Nitriles, such as acrylonitrile and methacrylonitrile, have beenindustrially produced as important intermediates for the preparation offibers, synthetic resins, synthetic rubbers, and the like. The mostpopular method for producing such nitrites is to subject an olefin suchas propene or isobutene to a gas phase catalytic reaction with ammoniaand oxygen in the presence of a catalyst at a high temperature. Knowncatalysts for conducting this reaction include a Mo—Bi—P—O catalyst, aV—Sb—O catalyst, an Sb—U—V—Ni—O catalyst, a Sb—Sn—O catalyst, aV—Sb—W—P—O catalyst and a catalyst obtained by mechanically mixing aV—Sb—W—O oxide and a Bi—Ce—Mo—W—O oxide. However, in view of the pricedifference between propane and propene or between isobutane andisobutene, attention has been drawn to the development of a method forproducing acrylonitrile or methacrylonitrile by an ammoxidation reactionwherein a lower alkane, such as propane or isobutane, is used as astarting material, and it is catalytically reacted with ammonia andoxygen in a gaseous phase in the presence of a catalyst.

In particular, U.S. Pat. No. 5,281,745 discloses a method for producingan unsaturated nitrile comprising subjecting an alkane and ammonia inthe gaseous state to catalytic oxidation in the presence of a catalystwhich satisfies the conditions:

(1) the mixed metal oxide catalyst is represented by the empiricalformulaMo_(a)V_(b)Te_(c)X_(x)O_(n)wherein X is at least one element selected from the group consisting ofniobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron and cerium and, when a=1, b=0.01 to1.0, c=0.01 to 1.0, x=0.01 to 1.0 and n is a number such that the totalvalency of the metal elements is satisfied; and

(2) the catalyst has X-ray diffraction peaks at the following angles(±0.3°) of 2θ in its X-ray diffraction pattern: 22.1°, 28.2°, 36.2°,45.2° and 50.0°.

Similarly, Japanese Laid-Open Patent Application Publication No.6-228073 discloses a method of nitrile preparation comprising reactingan alkane in a gas phase contact reaction with ammonia in the presenceof a mixed metal oxide catalyst of the formulaW_(a)V_(b)Te_(c)X_(x)O_(n)wherein X represents one or more elements selected from niobium,tantalum, titanium, aluminum, zirconium, chromium, manganese, iron,ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony,bismuth, indium and cerium and, when a=1, b=0.01 to 1.0, c=0.01 to 1.0,x=0.01 to 1.0 and n is determined by the oxide form of the elements.

Unsaturated carboxylic acids such as acrylic acid and methacrylic acidare industrially important as starting materials for various syntheticresins, coating materials and plasticizers. Commercially, the currentprocess for acrylic acid manufacture involves a two-step catalyticoxidation reaction starting with a propene feed. In the first stage,propene is converted to acrolein over a modified bismuth molybdatecatalyst. In the second stage, acrolein product from the first stage isconverted to acrylic acid using a catalyst composed of mainly molybdenumand vanadium oxides. In most cases, the catalyst formulations areproprietary to the catalyst supplier, but, the technology is wellestablished. Moreover, there is an incentive to develop a single stepprocess to prepare the unsaturated acid from its corresponding alkene.Therefore, the prior art describes cases where complex metal oxidecatalysts are utilized for the preparation of unsaturated acid from acorresponding alkene in a single step.

Japanese Laid-Open Patent Application Publication No. 07-053448discloses the manufacture of acrylic acid by the gas-phase catalyticoxidation of propene in the presence of mixed metal oxides containingMo, V, Te, O and X wherein X is at least one of Nb, Ta, W, Ti, Al, Zr,Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, Sb, Bi, B, In, Li, Na, K, Rb, Cs andCe.

Commercial incentives also exist for producing acrylic acid using alower cost propane feed. Therefore, the prior art describes caseswherein a mixed metal oxide catalyst is used to convert propane toacrylic acid in one step.

U.S. Pat. No. 5,380,933 discloses a method for producing an unsaturatedcarboxylic acid comprising subjecting an alkane to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containing amixed metal oxide comprising, as essential components, Mo, V, Te, O andX, wherein X is at least one element selected from the group consistingof niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron, indium and cerium; and wherein theproportions of the respective essential components, based on the totalamount of the essential components, exclusive of oxygen, satisfy thefollowing relationships:

0.25<r(Mo)<0.98, 0.003<r(V)<0.5, 0.003<r(Te)<0.5 and 0.003<r(X)<0.5,wherein r(Mo), r(V), r(Te) and r(X) are the molar fractions of Mo, V, Teand X, respectively, based on the total amount of the essentialcomponents exclusive of oxygen.

Nonetheless, the prior art continues to seek ways to improve theperformance of such mixed metal oxide catalysts. In particular, JapaneseLaid-Open Patent Application Publication No. 10-330343 discloses asingle stage washing or a dual stage washing followed by calcination ofa mixed metal oxide of the formulaMo_(a)V_(b)Sb_(c)X_(x)O_(n)

-   -   wherein X is at least one metal element selected from Ti, Zr,        Nb, Ta, Cr, W, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Zn,        In, Sn, Pb, Bi, Ce and alkaline earth metals,    -   wherein, when a=1, 0.02≦b≦0.99, 0.001≦c≦0.9, 0≦x≦0.89,        0.1≦c/b≦0.80 and n is a value determined by the oxidation state        of the other elements,        with solvents selected from aqueous oxalic acid, ethylene glycol        or aqueous hydrogen peroxide. The so-formed catalyst is used for        the ammoxidation of alkanes to form nitriles. Japanese Laid-Open        Patent Application Publication No. 11-043314 discloses the        washing of a mixed metal oxide of the formula        Mo_(a)V_(b)Sb_(c)X_(x)O_(n)    -   wherein X is at least one metal element selected from Ti, Zr,        Nb, Ta, Cr, W, Mn, Fe, Ru, Co, Rh, It, Ni, Pd, Pt, Cu, Ag, Zn,        In, Sn, Pb, Bi, Ce and alkaline earth metals,    -   wherein, when a=1, 0.02≦b≦0.99, 0.001≦c≦0.9, 0≦x≦0.89,        0.1≦c/b≦0.80 and n is a value determined by the oxidation state        of the other elements,        with at least one solvent selected from an aqueous solution of        an organic acid, an alcohol, an aqueous solution of an inorganic        acid or an aqueous solution of hydrogen peroxide, followed by        calcination. The so-formed material is indicated to be useful in        such applications as electronic materials, electrode materials,        mechanical inorganic materials and as catalysts in        petrochemistry, etc. In particular, use as a catalyst in the        oxidative dehydrogenation of ethane to produce ethylene is        exemplified.

It has now been found that the performance of a mixed metal oxidecatalyst having the empirical formulaA_(a)V_(b)N_(c)X_(d)O_(e)wherein

-   -   A is at least one element selected from the group consisting of        Mo and W, N is at least one element selected from the group        consisting of Te, Se and Sb, and X is at least one element        selected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr,        Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, Ce, As, Ge, Sn, Li, Na,        K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd,        Dy, Ho, Er, Tm, Yb and Lu,        wherein A, V, N and X are present in such amounts that the        atomic ratio of A:V:N:X is a:b:c:d, and        wherein, when a=1, b=0.01 to 2, c=0.01 to 1.0, d=0.01 to 1.0 and        e is dependent on the oxidation state of the other elements,        may be improved for the oxidation of an alkane, or a mixture of        an alkane and an alkene, to an unsaturated carboxylic acid or        may be improved for the ammoxidation of an alkane, or a mixture        of an alkane and an alkene, to an unsaturated nitrile, by        contacting the mixed metal oxide catalyst with a liquid contact        member selected from the group consisting of organic acids,        alcohols, inorganic acids and hydrogen peroxide, recovering        insoluble material from such contacting, followed by calcination        of recovered insoluble materials in a non-oxidizing atmosphere        and then promoting the so-formed catalyst with a promoter.

Thus, in a first aspect, the present invention provides a process forpreparing an improved catalyst, said process comprising:

-   -   (a) providing a mixed metal oxide having the empirical formula        A_(a)V_(b)N_(c)X_(d)O_(e)    -    wherein A is at least one element selected from the group        consisting of Mo and W, N is at least one element selected from        the group consisting of Te, Sb and Se, and X is at least one        element selected from the group consisting of Nb, Ta, Ti, Al,        Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, Ce, As, Ge, Sn,        Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm,        Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu,    -    wherein A, V, N and X are present in such amounts that the        atomic ratio of A:V:N:X is a:b:c:d, and    -    wherein, when a=1, b=0.01 to 2, c=0.01 to 1, d=0.01 to 1 and e        is dependent on the oxidation state of the other elements;    -   (b) contacting said mixed metal oxide with a liquid contact        member selected from the group consisting of organic acids,        alcohols, inorganic acids and hydrogen peroxide to form a        contact mixture;    -   (c) recovering insoluble material from said contact mixture; and    -   (d) calcining said recovered insoluble material in a        non-oxidizing atmosphere:    -   (e) admixing said calcined recovered insoluble material with        -   (i) at least one promoter element or compound thereof,            wherein said at least one promoter element is selected from            the group consisting of Au, Ag, Re, Pr, Zn, Ga, Pd, Ir, Nd,            Y, Sm, Th, Br, Cu, Sc, Cl, F and I, and        -   (ii) at least one solvent for said at least one promoter            element or compound thereof    -   to form an admixture;    -   (f) removing said at least one solvent from said so-formed        admixture to form a catalyst precursor;    -   (g) calcining said catalyst precursor.

In a second aspect, the present invention provides a further process forpreparing an improved catalyst, said process comprising:

-   -   (a) providing a mixed metal oxide having the empirical formula        A_(a)V_(b)N_(c)X_(d)O_(e)    -    wherein A is at least one element selected from the group        consisting of Mo and W, N is at least one element selected from        the group consisting of Te, Sb and Se, and X is at least one        element selected from the group consisting of Nb, Ta, Ti, Al,        Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, Ce, As, Ge, Sn,        Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm,        Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu,    -    wherein A, V, N and X are present in such amounts that the        atomic ratio of A:V:N:X is a:b:c:d, and    -    wherein, when a=1, b=0.01 to 2, c=0.01 to 1, d=0.01 to 1 and e        is dependent on the oxidation state of the other elements;    -   (b) contacting said mixed metal oxide with a liquid contact        member selected from the group consisting of organic acids,        alcohols, inorganic acids and hydrogen peroxide to form a        contact mixture;    -   (c) recovering insoluble material from said contact mixture; and    -   (d) calcining said recovered insoluble material in a        non-oxidizing atmosphere in the presence of a source of halogen.

In a third aspect, the present invention provides a still furtherprocess for preparing an improved catalyst, said process comprising:

-   -   a) providing a mixed metal oxide having the empirical formula        A_(a)V_(b)N_(c)X_(d)O_(e)    -    wherein A is at least one element selected from the group        consisting of Mo and W, N is at least one element selected from        the group consisting of Te, Sb and Se, and X is at least one        element selected from the group consisting of Nb, Ta, Ti, Al,        Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, Ce, As, Ge, Sn,        Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm,        Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu,    -    wherein A, V, N and X are present in such amounts that the        atomic ratio of A:V:N:X is a:b:c:d, and    -    wherein, when a=1, b=0.01 to 2, c=0.01 to 1, d=0.01 to 1 and e        is dependent on the oxidation state of the other elements;    -   (b) contacting said mixed metal oxide with a liquid contact        member selected from the group consisting of organic acids,        alcohols, inorganic acids and hydrogen peroxide to form a        contact mixture;    -   (c) recovering insoluble material from said contact mixture;    -   (d) calcining said recovered insoluble material in a        non-oxidizing atmosphere to form a calcined recovered insoluble        material; and    -   (e) contacting said calcined recovered insoluble material with a        source of halogen.

In fourth, fifth and sixth aspects, the present invention providescatalysts produced by the processes according to the first, second andthird aspects of the invention, respectively.

In seventh, eighth and ninth aspects, the present invention providesprocesses for producing an unsaturated carboxylic acid which comprisesubjecting an alkane, or a mixture of an alkane and an alkene, to avapor phase catalytic oxidation reaction in the presence of a catalystproduced by the processes according to the first, second and thirdaspects of the invention, respectively.

In tenth, eleventh and twelfth aspects, the present invention providesprocesses for producing an unsaturated nitrile which comprise subjectingan alkane, or a mixture of an alkane and an alkene, and ammonia to avapor phase catalytic oxidation reaction in the presence of a catalystproduced by the processes according to the first, second and thirdaspects of the invention, respectively.

The mixed metal oxide, which is used as the starting material for thepresent process of preparing an improved catalyst, is a mixed metaloxide that includes a material having the empirical formulaA_(a)V_(b)N_(c)X_(d)O_(e)wherein A is at least one element selected from the group consisting ofMo and W, N is at least one element selected from the group consistingof Te, Sb and Se, and X is at least one element selected from the groupconsisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb,Bi, B, In, Ce, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba,Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu; andwherein, when a=1, b=0.01 to 2, c=0.01 to 1.0, d=0.01 to 0.1 and e isdependent on the oxidation state of the other elements.

Preferably, when a=1, b=0.1 to 0.5, c=0.05 to 0.5 and d=0.01 to 0.5.More preferably, when a=1, b=0.15 to 0.45, c=0.05 to 0.45 and d=0.01 to0.1. The value of e, i.e. the amount of oxygen present, is dependent onthe oxidation state of the other elements in the catalyst. However, e istypically in the range of from 3 to 4.7.

For example, such a mixed metal oxide may be prepared by:

-   -   admixing compounds of elements A, V, N, X and at least one        solvent to form a mixture,    -    wherein A is at least one element selected from the group        consisting of Mo and W, N is at least one element selected from        the group consisting of Te, Sb and Se, and X is at least one        element selected from the group consisting of Nb, Ta, Ti, Al,        Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, Ce, As, Ge, Sn,        Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu,        Gd, Dy, Ho, Er, Tm, Yb and Lu,    -    wherein A, V, N and X are present in such amounts that the        atomic ratio of A:V:N:X is a:b:c:d, and    -    wherein, when a=1, b=0.01 to 2, c=0.01 to 1.0 and d=0.01 to        1.0;    -   removing the at least one solvent from the mixture to form a        precursor; and    -   calcining the precursor to form a mixed metal oxide.

Preferred mixed metal oxides have the empirical formulaeMo_(a)V_(b)Te_(c)Nb_(d)O_(e) and W_(a)V_(b)Te_(c)Nb_(d)O_(e) wherein a,b, c, d and e are as previously defined.

The mixed metal oxide to be used as the starting material may be anorthorhombic phase material.

In such a case, the orthorhombic phase mixed metal oxide may beprepared, for example, by the process comprising:

-   -   (a) providing a mixed metal oxide having the empirical formula        A_(a)V_(b)N_(c)X_(d)O_(e)    -    wherein A is at least one element selected from the group        consisting of Mo and W, N is at least one element selected from        the group consisting of Te, Sb and Se, and X is at least one        element selected from the group consisting of Nb, Ta, Ti, Al,        Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, Ce, As, Ge, Sn,        Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm,        Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu,    -    wherein A, V, N and X are present in such amounts that the        atomic ratio of A:V:N:X is a:b:c:d, and    -    wherein, when a=1, b=0.01 to 2, c=0.01 to 1, d=0.01 to 1 and e        is dependent on the oxidation state of the other elements;    -   (b) contacting said mixed metal oxide with a liquid contact        member selected from the group consisting of organic acids,        alcohols, inorganic acids and hydrogen peroxide to form a        contact mixture; and    -   (c) recovering insoluble material from said contact mixture to        obtain said orthorhombic phase mixed metal oxide.

Alternatively, such an orthorhombic phase mixed metal oxide may beprepared, for example, by a process comprising:

-   -   (a) admixing compounds of elements A, V, N and X and at least        one solvent to form a solution,    -    wherein A is at least one element selected from the group        consisting of Mo and W, N is at least one element selected from        the group consisting of Te, Sb and Se, and X is at least one        element selected from the group consisting of Nb, Ta, Ti, Al,        Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, Ce, As, Ge, Sn,        Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm,        Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu,    -    wherein A, V, N and X are present in such amounts that the        atomic ratio of A:V:N:X is a:b:c:d, and    -    wherein, when a=1, b=0.01 to 2, c=0.01 to 1.0 and d=0.01 to        1.0;    -   (b) admixing a seeding effective amount of an orthorhombic phase        mixed metal oxide seed, substantially free of hexagonal phase        mixed metal oxide, with said solution to form a seeded solution;    -   (c) removing said at least one solvent from said seeded solution        to form a catalyst precursor; and    -   (d) calcining said catalyst precursor to obtain said        orthorhombic phase mixed metal oxide.

By a seeding effective amount is meant an amount of seed materialeffective to cause nucleation of the orthorhombic phase, e.g., 0.01% byweight of seed material based on the total weight of the solution beingseeded. By an orthorhombic phase mixed metal oxide which issubstantially free of hexagonal phase mixed metal oxide is meant amaterial that contains not less than 90% by weight of orthorhombic phasebased on the total weight of the material.

The orthorhombic phase mixed metal oxide substantially free of hexagonalphase mixed metal oxide, to be used as seed, may be prepared, forexample, by:

-   -   taking a mixed metal oxide having the empirical formula         A_(a)V_(b)N_(c)X_(d)O_(e)    -    wherein A is at least one element selected from the group        consisting of Mo and W, N is at least one element selected from        the group consisting of Te, Sb and Se, and X is at least one        element selected from the group consisting of Nb, Ta, Ti, Al,        Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, Ce, As, Ge, Sn,        Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm,        Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu,    -    wherein, when a=1, b=0.01 to 2, c=0.01 to 1.0, d=0.01 to 1.0        and e is dependent on the oxidation state of the other elements;    -   contacting the mixed metal oxide with a liquid contacting member        selected from the group consisting of organic acids, alcohols,        inorganic acids and hydrogen peroxide to form a contact mixture;        and    -   recovering insoluble material, to be used as seed material, from        the contact mixture.

Alternatively, the orthorhombic phase mixed metal oxide substantiallyfree of hexagonal phase mixed metal oxide, to be used as seed, may beprepared, for example, by:

-   -   admixing compounds of elements A, V, N and X and at least one        solvent to form a mixture    -    wherein A is at least one element selected from the group        consisting of Mo and W, N is at least one element selected from        the group consisting of Te, Sb and Se, and X is at least one        element selected from the group consisting of Nb, Ta, Ti, Al,        Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, Ce, As, Ge, Sn,        Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm,        Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu,    -    wherein A, V, N and X are present in such amounts that the        atomic ratio of A:V:N:X is a:b:c:d, and    -    wherein, when a=1, b=0.01 to 2, c=0.01 to 1.0 and d=0.01 to        1.0;    -   removing the at least one solvent from the mixture to form a        precursor; calcining the precursor to form a calcined precursor;    -   contacting the calcined precursor with a liquid contact member        selected from the group consisting of organic acids, alcohols,        inorganic acids and hydrogen peroxide to form a contact mixture;        and    -   recovering insoluble material, to be used as seed material, from        the contact mixture.

Suitable solvents, for the above-noted processes, include water;alcohols including, but not limited to, methanol, ethanol, propanol, anddiols, etc.; as well as other polar solvents known in the art.Generally, water is preferred. The water is any water suitable for usein chemical syntheses including, without limitation, distilled water andde-ionized water. The amount of water present is preferably an amountsufficient to keep the elements substantially in solution long enough toavoid or minimize compositional and/or phase segregation during thepreparation steps. Accordingly, the amount of water will vary accordingto the amounts and solubilities of the materials combined. However, theamount of water is preferably sufficient to ensure an aqueous solutionis formed, at the time of mixing.

The solvent is removed by any suitable method, known in the art, to forma catalyst precursor. Such methods include, without limitation, vacuumdrying, freeze drying, spray drying, rotary evaporation and air drying.

For example, in the case of water being the solvent: Vacuum drying isgenerally performed at pressures ranging from 10 mmHg to 500 mmHg.Freeze drying typically entails freezing the solution, using, forinstance, liquid nitrogen, and drying the frozen solution under vacuum.Spray drying is generally performed under an inert atmosphere such asnitrogen or argon, with an inlet temperature ranging from 125° C. to200° C. and an outlet temperature ranging from 75° C. to 150° C. Rotaryevaporation is generally performed at a bath temperature of from 25° C.to 90° C. and at a pressure of from 10 mmHg to 760 mmHg, preferably at abath temperature of from 40° to 90° C. and at a pressure of from 10 mmHgto 350 mmHg, more preferably at a bath temperature of from 40° C. to 60°C. and at a pressure of from 10 mmHg to 40 mmHg. Air drying may beeffected at temperatures ranging from 25° C. to 90° C. Rotaryevaporation or air drying are generally preferred.

Contacting with a liquid contact member selected from the groupconsisting of organic acids, alcohols, inorganic acids and hydrogenperoxide (whether it be for the purpose of making the final catalyst, anorthorhombic phase mixed metal oxide, or for the purpose of making aseed material) may be effected without any particular restrictions (solong as, in the case of the preparation of the orthorhombic phase mixedmetal oxide, the hexagonal phase is fully removed from the mixed metaloxide or the calcined precursor). In this regard, the liquid contactmember is normally used in an amount of 1 to 100 times the volume of themixed metal oxide or the first calcined precursor, preferably 3 to 50times the volume, more preferably 5 to 25 times the volume. (Contactingat elevated temperatures will remove the hexagonal phase more rapidly.However, if prolonged contact time is not a consideration, contacting atroom temperature may be utilized.) Normally, contact temperatures ofroom temperature to 100° C. are utilized, preferably 50° C. to 90° C.,more preferably 60° C. to 80° C. As previously noted, contact time willbe affected by the temperature at which the contacting is carried out.Normally, contact times of 1 to 100 hours are utilized, preferably 2 to20 hours, more preferably 5 to 10 hours. The contact mixture ispreferably agitated during the contacting.

There are no particular restrictions upon the organic acids which may beused as the liquid contacting member. For example, oxalic acid, formicacid, acetic acid, citric acid and tartaric acid may be used, however,oxalic acid is preferred. If the organic acid is a liquid, it may beused as is or in an aqueous solution. If the organic acid is a solid, itis used in an aqueous solution. When using aqueous solutions, there areno particular restrictions on the concentration of the organic acid.Normally, the concentration of the organic acid in the aqueous solutioncan vary from 0.1 to 50% by weight, preferably 1 to 15% by weight.

There are no particular restrictions upon the alcohols which may be usedas the liquid contacting member. For example, methanol, ethanol,propanol, butanol, hexanol and diols may be utilized, however, alcoholshaving one to four carbon atoms are preferred, with ethylene glycolbeing particularly preferred. The alcohols may be utilized in the formof aqueous solutions, but, if so, the water content should be held to20% by weight or less for the best effectiveness.

Similarly, there are no particular restrictions upon the inorganic acidswhich may be used as the liquid contacting member. For example, telluricacid, nitric acid, sulfuric acid, phosphoric acid, hydrochloric acid,perchloric acid, chloric acid and hypochlorous acid may be used. Theinorganic acids are typically used as aqueous solutions withconcentrations of the acids in the range of from 0.1 to 50% by weight,preferably from 0.1 to 10% by weight.

When hydrogen peroxide is utilized as the liquid contacting member, itis used in the form of an aqueous solution having a concentration in therange of from 0.1 to 50% by weight, preferably from 1 to 10% by weight.

After contacting with the liquid contacting member, insoluble materialis recovered from the so-formed contact mixture. The insoluble materialmay be recovered by any conventional method, e.g., centrifugation orfiltration. If the contacting was conducted at elevated temperature, thecontact mixture may be cooled prior to recovery of the insolublematerial. If desired, the recovered insoluble material may be washedwith one of the previously disclosed solvents, preferably water.

Calcination may be conducted in an oxidizing atmosphere, e.g., in air,oxygen-enriched air or oxygen, or in the substantial absence of oxygen,e.g., in an inert atmosphere or in vacuo. The inert atmosphere may beany material which is substantially inert, i.e., does not react orinteract with, the catalyst precursor. Suitable examples include,without limitation, nitrogen, argon, xenon, helium or mixtures thereof.Preferably, the inert atmosphere is argon or nitrogen, more preferablyargon. The inert atmosphere may flow over the surface of the catalystprecursor or may not flow thereover (a static environment). When theinert atmosphere does flow over the surface of the catalyst precursor,the flow rate can vary over a wide range, e.g., at a space velocity offrom 1 to 500 hr⁻¹.

The calcination is usually performed at a temperature of from 350° C. to850° C., preferably from 400° C. to 700° C., more preferably from 500°C. to 640° C. The calcination is performed for an amount of timesuitable to form the aforementioned catalyst. Typically, the calcinationis performed for from 0.5 to 30 hours, preferably from 1 to 25 hours,more preferably for from 1 to 15 hours, to obtain the desired promotedmixed metal oxide.

In a preferred mode of operation, calcination is conducted in twostages. In the first stage, the catalyst precursor is calcined in anoxidizing environment (e.g. air) at a temperature of from 200° C. to400° C., preferably from 275° C. to 325° C. for from 15 minutes to 8hours, preferably for from 1 to 3 hours. In the second stage, thematerial from the first stage is calcined in a non-oxidizing environment(e.g., an inert atmosphere) at a temperature of from 500° C. to 750° C.,preferably for from 550° C. to 650° C., for 15 minutes to 8 hours,preferably for from 1 to 3 hours. Optionally, a reducing gas, such as,for example, ammonia or hydrogen, may be added during the second stagecalcination.

In a particularly preferred mode of operation, in the first stage, thematerial to be calcined is placed in the desired oxidizing atmosphere atroom temperature and then raised to the first stage calcinationtemperature and held there for the desired first stage calcination time.The atmosphere is then replaced with the desired non-oxidizingatmosphere for the second stage calcination, the temperature is raisedto the desired second stage calcination temperature and held there forthe desired second stage calcination time.

In an another preferred mode of operation, the insoluble materialrecovered from the contact mixture is calcined in a non-oxidizingatmosphere, preferably an inert atmosphere. In the case where thepromoter element is a halogen, such halogen may be added to theaforementioned non-oxidizing atmosphere.

Although any type of heating mechanism, e.g., a furnace, may be utilizedduring the calcination, it is preferred to conduct the calcination undera flow of the designated gaseous environment. Therefore, it isadvantageous to conduct the calcination in a bed with continuous flow ofthe desired gas(es) through the bed of solid catalyst precursorparticles.

When the present invention requires calcination in a non-oxidizingatmosphere, the calcination is conducted in an inert atmosphere or invacuo, preferably, in an inert atmosphere. The inert atmosphere may beany material which is substantially inert to, i.e. does not react orinteract with, the material being calcined. Suitable examples include,without limitation, nitrogen, argon, xenon, helium or mixtures thereof.Preferably the inert gas is argon or nitrogen. Preferably, the inertatmosphere flows over the surface of the material to be calcined. Whilethe flow rate may vary over a wide range, typically, a space velocity offrom 1 to 500 hr⁻¹ may be utilized. The calcination in a non-oxidizingatmosphere is usually performed at a temperature of from 350° C. to 850°C., preferably from 400° C. to 700° C., more preferably from 500° C. to640° C. The calcination in a non-oxidizing atmosphere is typicallyperformed for from 0.5 to 20 hours, preferably for from 1 to 10 hours,more preferably for from 1 to 5 hours. In the calcination in anon-oxidizing atmosphere, the material to be calcined is preferablyplaced under the inert atmosphere at room temperature, then raised tothe desired calcination temperature while under the inert atmosphere,and then maintained at the desired calcination temperature for thedesired time of calcination. Typically, after calcination the calcinedmaterial is allowed to cool while being maintained under the inertatmosphere.

The starting materials for the above mixed metal oxide are notparticularly limited. A wide range of materials including, for example,oxides, nitrates, halides or oxyhalides, alkoxides, acetylacetonates,and organometallic compounds may be used. For example, ammoniumheptamolybdate may be utilized for the source of molybdenum in thecatalyst. However, compounds such as MoO₃, MoO₂, MoCl₅, MoOCl₄,Mo(OC₂H₅)₅, molybdenum acetylacetonate, phosphomolybdic acid andsilicomolybdic acid may also be utilized instead of ammoniumheptamolybdate. Similarly, ammonium metavanadate may be utilized for thesource of vanadium in the catalyst. However, compounds such as V₂O₅,V₂O₃, VOCl₃, VCl₄, VO(OC₂H₅)₃, vanadium acetylacetonate and vanadylacetylacetonate may also be utilized instead of ammonium metavanadate.The tellurium source may include telluric acid, TeCl₄, Te(OC₂H₅)₅,Te(OCH(CH₃)₂)₄ and TeO₂. The niobium source may include ammonium niobiumoxalate, Nb₂O₅, NbCl₅, niobic acid or Nb(OC₂H₅)₅ as well as the moreconventional niobium oxalate.

With respect to the promoter elements or compounds thereof that may beutilized to make the improved catalysts of the present invention, noparticular restrictions are placed thereon. With this in mind, thefollowing lists are merely illustrative of available sources of theseelements or the compounds thereof, not limiting thereon.

The gold source may be ammonium tetrachloroaurate, gold bromide, goldchloride, gold cyanide, gold hydroxide, gold iodide, gold oxide, goldtrichloride acid or gold sulfide.

The silver source may be silver acetate, silver acetylacetonate, silverbenzoate, silver bromide, silver carbonate, silver chloride, silvercitrate hydrate, silver fluoride, silver iodide, silver lactate, silvernitrate, solver nitrite, silver oxide, silver phosphate, or a solutionof silver in an aqueous inorganic acid, e.g., nitric acid.

The copper source may be copper acetate, copper acetate monohydrate,copper acetate hydrate, copper acetylacetonate, copper bromide, coppercarbonate, copper chloride, copper chloride dihydrate, copper fluoride,copper formate hydrate, copper gluconate, copper hydroxide, copperiodide, copper methoxide, copper nitrate hydrate, copper nitrate, copperoxide, copper tartrate hydrate, or a solution of copper in an aqueousinorganic acid, e.g., nitric acid.

The praseodymium source may be praseodymium (III) acetate, praseodymium(III) acetylacetonate, praseodymium (III) bromide, praseodymium (III)carbonate, praseodymium (III) chloride, praseodymium (III) fluoride,praseodymium (III) hexafluoroacetylacetonate, praseodymium (III) iodide,praseodymium (III) isopropoxide, praseodymium (III) nitrate,praseodymium (III) oxalate, praseodymium (III) oxide, praseodymium (III)perchlorate, praseodymium (III) sulfate, praseodymium (III) triflate orpraseodymium (III) trifluoromethane sulfate.

The terbium source may be a solution of terbium in an aqueous inorganicacid, e.g., nitric acid.

The neodymium source may be a neodymium salt, e.g., neodymium nitrate,dissolved in an aqueous inorganic acid, e.g. nitric acid.

The yittrium source may be an yittrium salt, e.g., yittrium nitrate,dissolved in water.

The scandium source may be scandium acetate, scandium bromide hydrate,scandium chloride, scandium chloride hexahydrate, scandium chloridehydrate, scandium fluoride, scandium iodide, scandium isopropoxide,scandium nitrate hydrate, scandium oxalate hydrate, scandium oxide, or asolution of scandium in an aqueous inorganic acid, e.g., nitric acid.

The rhenium source may be ammonium perrhenate, rhenium carbonyl, rheniumchloride, rhenium fluoride, rhenium oxide, rhenium pentacarbonylbromide, rhenium pentacarbonyl chloride and rhenium sulfide.

The palladium source may be palladium nitrate, palladium (II) acetate,palladium oxalate, palladium oxide, palladium hydroxide, palladiumchloride, palladium acetylacetonate or palladium metal.

The iridium source may be iridium acetylacetonate, iridium bromidehydrate, iridium chloride, iridium chloride hydrochloride hydrate,iridium chloride hydrate, iridium oxide, iridium oxide hydrate, iridiumoxoacetate trihydrate or iridium dissolved in an aqueous inorganic acid,e.g., nitric acid.

The samarium source may be samarium (III) acetate hydrate, samarium(III) acetylacetonate hydrate, samarium (II) bromide, samarium (III)bromide, samarium (III) bromide hexahydrate, samarium (III) carbonatehydrate, samarium (II) chloride, samarium (III) chloride, samarium (III)chloride hexahydrate, samarium (III) fluoride, samarium (II) iodide,samarium (III) iodide, samarium (III) isopropoxide, samarium (III)nitrate hexahydrate, samarium (III) oxalate hydrate, samarium (III)oxide or a solution of samarium in an aqueous inorganic acid, e.g.,nitric acid.

The zinc source may be zinc acetate, zinc acetylacetonate, zincacrylate, zinc bis(2,2,6,6-tetramethyl-3,5-heptanedioate), zinc bromide,zinc carbonate hydroxide, zinc chloride, zinc citrate, zinccyclohexanebutyrate, zinc 3,5-di-tert-butylsalicylate, zinc fluoride,zinc iodide, zinc L-lactate, zinc methacrylate, zinc nitrate, zincoxide, zinc perchlorate or zinc stearate.

The gallium source may be Ga₂O, GaCl₃, GaCl₂, gallium acetylacetonate,Ga₂O₃ or Ga(NO₃)₃.

The bromine source may be added as one of the above reagents as abromide, e.g., as the bromide salt of X (where X is at least one elementselected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe,Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb, Cs, Fr,Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb andLu), for example, as molybdenum bromide, tellurium tetrabromide, niobiumbromide or vanadium bromide; or as a solution of bromine in an aqueousinorganic acid, e.g., nitric acid. The bromine source may also be addedduring the calcination of the recovered insoluble material or, aftercalcination, as a bromine treatment step. For example, the brominesource may be added to the calcination atmosphere or to the oxidation orammoxidation reactor feed stream, as, for example, HBr, Br₂, ethylbromide or the like, to achieve a promotional effect with the bromine.

The chlorine source may also be added as one of the above reagents as achloride, e.g., as the chloride salt of X (where X is at least oneelement selected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr,Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb,Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm,Yb and Lu), for example, as molybdenum chloride, telluriumtetrachloride, niobium chloride or vanadium chloride. The chlorinesource may also be added during the calcination of the recoveredinsoluble material or, after calcination, as a chlorine treatment step.For example, the chlorine source may be added to the calcinationatmosphere or to the oxidation or ammoxidation reactor feed stream, as,for example, HCl, Cl₂, ethyl chloride or the like, to achieve apromotional effect with the chloride.

The fluorine source may be added as one of the above reagents as afluoride, e.g., as the fluoride salt of X (where X is at least oneelement selected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr,Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb,Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm,Yb and Lu), for example, as molybdenum fluoride, tellurium fluoride,niobium fluoride or vanadium fluoride. The fluorine source may also beadded during the calcination of the recovered insoluble material or,after calcination, as a fluorine treatment step. For example, thefluorine source may be added to the calcination atmosphere or to theoxidation or ammoxidation reactor feed stream, as, for example, HF, F₂,ethyl fluoride or the like, to achieve a promotional effect with thefluoride.

The iodine source may be added as one of the above reagents as afluoride, e.g., as the fluoride salt of X (where X is at least oneelement selected from the group consisting of Nb, Ta, Ti, Al, Zr, Cr,Mn, Fe, Ru, Co, Rh, Ni, Pt, Sb, Bi, B, In, As, Ge, Sn, Li, Na, K, Rb,Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm,Yb and Lu), for example, as molybdenum iodide, tellurium iodide, niobiumiodide or vanadium iodide. The iodine source may also be added duringthe calcination of the recovered insoluble material or, aftercalcination, as an iodine treatment step. For example, the iodine sourcemay be added to the calcination atmosphere or to the oxidation orammoxidation reactor feed stream, as, for example, HI, I₂, ethyl iodideor the like, to achieve a promotional effect with the iodide.

The promoter element(s) or the compounds thereof are added in amounts soas to achieve a level of promoter element in the improved catalyst suchthat the atomic ratio of promoter element:element(s) A is 0.001 to 1:1,preferably 0.001 to 0.1:1.

The improved catalyst formed by the aforementioned techniques, exhibitsexcellent catalytic activities by itself. However, the mixed metal oxidemay be converted to a catalyst having higher activities by grinding.

There is no particular restriction as to the grinding method, andconventional methods may be employed. As a dry grinding method, a methodof using a gas stream grinder may, for example, be mentioned whereincoarse particles are permitted to collide with one another in a highspeed gas stream for grinding. The grinding may be conducted not onlymechanically but also by using a mortar or the like in the case of asmall scale operation.

As a wet grinding method wherein grinding is conducted in a wet state byadding water or an organic solvent to the above mixed metal oxide, aconventional method of using a rotary cylinder-type medium mill or amedium-stirring type mill, may be mentioned. The rotary cylinder-typemedium mill is a wet mill of the type wherein a container for the objectto be ground is rotated, and it includes, for example, a ball mill and arod mill. The medium-stirring type mill is a wet mill of the typewherein the object to be ground, contained in a container is stirred bya stirring apparatus, and it includes, for example, a rotary screw typemill, and a rotary disc type mill.

The conditions for grinding may suitably be set to meet the nature ofthe above-mentioned promoted mixed metal oxide, the viscosity, theconcentration, etc. of the solvent used in the case of wet grinding, orthe optimum conditions of the grinding apparatus. However, it ispreferred that grinding is conducted until the average particle size ofthe ground catalyst precursor would usually be at most 20 μm, morepreferably at most 5 μm. Improvement in the catalytic performance mayoccur due to such grinding.

Further, in some cases, it is possible to further improve the catalyticactivities by further adding a solvent to the ground catalyst precursorto form a solution or slurry, followed by drying again. There is noparticular restriction as to the concentration of the solution orslurry, and it is usual to adjust the solution or slurry so that thetotal amount of the starting material compounds for the ground catalystprecursor is from 10 to 60 wt %. Then, this solution or slurry is driedby a method such as spray drying, freeze drying, evaporation to drynessor vacuum drying, preferably by the spray drying method. Further,similar drying may be conducted also in the case where wet grinding isconducted.

The oxide obtained by the above-mentioned method may be used as a finalcatalyst, but it may further be subjected to heat treatment usually at atemperature of from 200° to 700° C. for from 0.1 to 10 hours.

The mixed metal oxide thus obtained may be used by itself as a solidcatalyst, but may be formed into a catalyst together with a suitablecarrier such as silica, alumina, titania, aluminosilicate, diatomaceousearth or zirconia. Further, it may be molded into a suitable shape andparticle size depending upon the scale or system of the reactor.

In its seventh, eighth and ninth aspects, the present invention providesprocesses for producing an unsaturated carboxylic acid, which comprisesubjecting an alkane, or a mixture of an alkane and an alkene, to avapor phase catalytic oxidation reaction in the presence of a catalystproduced in accord with the present invention to produce an unsaturatedcarboxylic acid.

In the production of such an unsaturated carboxylic acid, it ispreferred to employ a starting material gas which contains steam. Insuch a case, as a starting material gas to be supplied to the reactionsystem, a gas mixture comprising a steam-containing alkane, or asteam-containing mixture of alkane and alkene, and an oxygen-containinggas, is usually used. However, the steam-containing alkane, or thesteam-containing mixture of alkane and alkene, and the oxygen-containinggas may be alternately supplied to the reaction system. The steam to beemployed may be present in the form of steam gas in the reaction system,and the manner of its introduction is not particularly limited.

In regard to the use of a halogen as the promoter element of thecatalyst of the present invention, it is possible to add a gaseoushalogen source as previously identified to the gas feed to the reaction.

Further, as a diluting gas, an inert gas such as nitrogen, argon orhelium may be supplied. The molar ratio (alkane or mixture of alkane andalkene):(oxygen):(diluting gas):(H₂O) in the starting material gas ispreferably (1):(0.1 to 10):(0 to 20):(0.2 to 70), more preferably (1):(1to 5.0):(0 to 10):(5 to 40).

When steam is supplied together with the alkane, or the mixture ofalkane and alkene, as starting material gas, the selectivity for anunsaturated carboxylic acid is distinctly improved, and the unsaturatedcarboxylic acid can be obtained from the alkane, or mixture of alkaneand alkene, in good yield simply by contacting in one stage. However,the conventional technique utilizes a diluting gas such as nitrogen,argon or helium for the purpose of diluting the starting material. Assuch a diluting gas, to adjust the space velocity, the oxygen partialpressure and the steam partial pressure, an inert gas such as nitrogen,argon or helium may be used together with the steam.

As the starting material alkane it is preferred to employ a C₃₋₈alkane,particularly propane, isobutane or n-butane; more preferably, propane orisobutane; most preferably, propane. According to the present invention,from such an alkane, an unsaturated carboxylic acid such as anα,β-unsaturated carboxylic acid can be obtained in good yield. Forexample, when propane or isobutane is used as the starting materialalkane, acrylic acid or methacrylic acid will be obtained, respectively,in good yield.

In the present invention, as the starting material mixture of alkane andalkene, it is possible to employ a mixture of C₃₋₈alkane and C₃₋₈alkene,particularly propane and propene, isobutane and isobutene or n-butaneand n-butene. As the starting material mixture of alkane and alkene,propane and propene or isobutane and isobutene are more preferred. Mostpreferred is a mixture of propane and propene. According to the presentinvention, from such a mixture of an alkane and an alkene, anunsaturated carboxylic acid such as an α,β-unsaturated carboxylic acidcan be obtained in good yield. For example, when propane and propene orisobutane and isobutene are used as the starting material mixture ofalkane and alkene, acrylic acid or methacrylic acid will be obtained,respectively, in good yield. Preferably, in the mixture of alkane andalkene, the alkene is present in an amount of at least 0.5% by weight,more preferably at least 1.0% by weight to 95% by weight; mostpreferably, 3% by weight to 90% by weight.

As an alternative, an alkanol, such as isobutanol, which will dehydrateunder the reaction conditions to form its corresponding alkene, i.e.isobutene, may also be used as a feed to the present process or inconjunction with the previously mentioned feed streams.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material alkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the oxidation reaction of the presentinvention is not clearly understood, but the oxidation reaction iscarried out by oxygen atoms present in the above promoted mixed metaloxide or by molecular oxygen present in the feed gas. To incorporatemolecular oxygen into the feed gas, such molecular oxygen may be pureoxygen gas. However, it is usually more economical to use anoxygen-containing gas such as air, since purity is not particularlyrequired.

It is also possible to use only an alkane, or a mixture of alkane andalkene, substantially in the absence of molecular oxygen for the vaporphase catalytic reaction. In such a case, it is preferred to adopt amethod wherein a part of the catalyst is appropriately withdrawn fromthe reaction zone from time to time, then sent to an oxidationregenerator, regenerated and then returned to the reaction zone forreuse. As the regeneration method of the catalyst, a method may, forexample, be mentioned which comprises contacting an oxidative gas suchas oxygen, air or nitrogen monoxide with the catalyst in the regeneratorusually at a temperature of from 300° to 600° C.

These aspects of the present invention will be described in furtherdetail with respect to a case where propane is used as the startingmaterial alkane and air is used as the oxygen source. The reactionsystem may be a fixed bed system or a fluidized bed system. However,since the reaction is an exothermic reaction, a fluidized bed system maypreferably be employed whereby it is easy to control the reactiontemperature. The proportion of air to be supplied to the reaction systemis important for the selectivity for the resulting acrylic acid, and itis usually at most 25 moles, preferably from 0.2 to 18 moles per mole ofpropane, whereby high selectivity for acrylic acid can be obtained. Thisreaction can be conducted usually under atmospheric pressure, but may beconducted under a slightly elevated pressure or slightly reducedpressure. With respect to other alkanes such as isobutane, or tomixtures of alkanes and alkenes such as propane and propene, thecomposition of the feed gas may be selected in accordance with theconditions for propane.

Typical reaction conditions for the oxidation of propane or isobutane toacrylic acid or methacrylic acid may be utilized in the practice of thepresent invention. The process may be practiced in a single pass mode(only fresh feed is fed to the reactor) or in a recycle mode (at least aportion of the reactor effluent is returned to the reactor). Generalconditions for the process of the present invention are as follows: thereaction temperature can vary from 200° C. to 700° C., but is usually inthe range of from 200° C. to 550° C., more preferably 250° C. to 480°C., most preferably 300° C. to 400° C.; the gas space velocity, SV, inthe vapor phase reaction is usually within a range of from 100 to 10,000hr⁻¹, preferably 300 to 6,000 hr⁻¹, more preferably 300 to 2,000 hr⁻¹;the average contact time with the catalyst can be from 0.01 to 10seconds or more, but is usually in the range of from 0.1 to 10 seconds,preferably from 2 to 6 seconds; the pressure in the reaction zoneusually ranges from 0 to 75 psig, but is preferably no more than 50psig. In a single pass mode process, it is preferred that the oxygen besupplied from an oxygen-containing gas such as air. The single pass modeprocess may also be practiced with oxygen addition. In the practice ofthe recycle mode process, oxygen gas by itself is the preferred sourceso as to avoid the build up of inert gases in the reaction zone.

Of course, in the oxidation reaction of the present invention, it isimportant that the hydrocarbon and oxygen concentrations in the feedgases be maintained at the appropriate levels to minimize or avoidentering a flammable regime within the reaction zone or especially atthe outlet of the reactor zone. Generally, it is preferred that theoutlet oxygen levels be low to both minimize after-burning and,particularly, in the recycle mode of operation, to minimize the amountof oxygen in the recycled gaseous effluent stream. In addition,operation of the reaction at a low temperature (below 450° C.) isextremely attractive because after-burning becomes less of a problemwhich enables the attainment of higher selectivity to the desiredproducts. The catalyst of the present invention operates moreefficiently at the lower temperature range set forth above,significantly reducing the formation of acetic acid and carbon oxides,and increasing selectivity to acrylic acid. As a diluting gas to adjustthe space velocity and the oxygen partial pressure, an inert gas such asnitrogen, argon or helium may be employed.

When the oxidation reaction of propane, and especially the oxidationreaction of propane and propene, is conducted by the method of thepresent invention, carbon monoxide, carbon dioxide, acetic acid, etc.may be produced as by-products, in addition to acrylic acid. Further, inthe method of the present invention, an unsaturated aldehyde maysometimes be formed depending upon the reaction conditions. For example,when propane is present in the starting material mixture, acrolein maybe formed; and when isobutane is present in the starting materialmixture, methacrolein may be formed. In such a case, such an unsaturatedaldehyde can be converted to the desired unsaturated carboxylic acid bysubjecting it again to the vapor phase catalytic oxidation with thepromoted mixed metal oxide-containing catalyst of the present inventionor by subjecting it to a vapor phase catalytic oxidation reaction with aconventional oxidation reaction catalyst for an unsaturated aldehyde.

In its tenth, eleventh and twelfth aspects, the present inventionprovides processes for producing an unsaturated nitrile, which comprisessubjecting an alkane, or a mixture of an alkane and an alkene, to avapor phase catalytic oxidation reaction with ammonia in the presence ofa catalyst produced in accord with the present invention to produce anunsaturated nitrile.

In regard to the use of a halogen as the promoter element of thecatalyst of the present invention, it is possible to add a gaseoushalogen source as previously identified to the gas feed to the reaction.

In the production of such an unsaturated nitrile, as the startingmaterial alkane, it is preferred to employ a C₃₋₈alkane such as propane,butane, isobutane, pentane, hexane and heptane. However, in view of theindustrial application of nitrites to be produced, it is preferred toemploy a lower alkane having 3 or 4 carbon atoms, particularly propaneand isobutane.

Similarly, as the starting material mixture of alkane and alkene, it ispossible to employ a mixture of C₃₋₈alkane and C₃₋₈alkene such aspropane and propene, butane and butene, isobutane and isobutene, pentaneand pentene, hexane and hexene, and heptane and heptene. However, inview of the industrial application of nitriles to be produced, it ismore preferred to employ a mixture of a lower alkane having 3 or 4carbon atoms and a lower alkene having 3 or 4 carbon atoms, particularlypropane and propene or isobutane and isobutene. Preferably, in themixture of alkane and alkene, the alkene is present in an amount of atleast 0.5% by weight, more preferably at least 1.0% by weight to 95% byweight, most preferably 3% by weight to 90% by weight.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material alkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the ammoxidation reaction of this aspect ofthe present invention is not clearly understood. However, the oxidationreaction is conducted by the oxygen atoms present in the above promotedmixed metal oxide or by the molecular oxygen in the feed gas. Whenmolecular oxygen is incorporated in the feed gas, the oxygen may be pureoxygen gas. However, since high purity is not required, it is usuallyeconomical to use an oxygen-containing gas such as air.

As the feed gas, it is possible to use a gas mixture comprising analkane, or a mixture of an alkane and an alkene, ammonia and anoxygen-containing gas, However, a gas mixture comprising an alkane or amixture of an alkane and an alkene and ammonia, and an oxygen-containinggas may be supplied alternately.

When the gas phase catalytic reaction is conducted using an alkane, or amixture of an alkane and an alkene, and ammonia substantially free frommolecular oxygen, as the feed gas, it is advisable to employ a methodwherein a part of the catalyst is periodically withdrawn and sent to anoxidation regenerator for regeneration, and the regenerated catalyst isreturned to the reaction zone. As a method for regenerating thecatalyst, a method may be mentioned wherein an oxidizing gas such asoxygen, air or nitrogen monoxide is permitted to flow through thecatalyst in the regenerator usually at a temperature of from 300° C. to600° C.

These aspects of the present invention will be described in furtherdetail with respect to a case where propane is used as the startingmaterial alkane and air is used as the oxygen source. The proportion ofair to be supplied for the reaction is important with respect to theselectivity for the resulting acrylonitrile. Namely, high selectivityfor acrylonitrile is obtained when air is supplied within a range of atmost 25 moles, particularly 1 to 15 moles, per mole of the propane. Theproportion of ammonia to be supplied for the reaction is preferablywithin a range of from 0.2 to 5 moles, particularly from 0.5 to 3 moles,per mole of propane. This reaction may usually be conducted underatmospheric pressure, but may be conducted under a slightly increasedpressure or a slightly reduced pressure. With respect to other alkanessuch as isobutane, or to mixtures of alkanes and alkenes such as propaneand propene, the composition of the feed gas may be selected inaccordance with the conditions for propane.

The processes of these aspects of the present invention may be conductedat a temperature of, for example, from 250° C. to 480° C. Morepreferably, the temperature is from 300° C. to 400° C. The gas spacevelocity, SV, in the gas phase reaction is usually within the range offrom 100 to 10,000 hr⁻¹, preferably from 300 to 6,000 hr⁻¹, morepreferably from 300 to 2,000 hr⁻¹. As a diluent gas, for adjusting thespace velocity and the oxygen partial pressure, an inert gas such asnitrogen, argon or helium can be employed. When ammoxidation of propaneis conducted by the method of the present invention, in addition toacrylonitrile, carbon monoxide, carbon dioxide, acetonitrile,hydrocyanic acid and acrolein may form as by-products.

EXAMPLES Preparative Comparative Example 1

In a 2000 mL rotavap flask containing 300 g of water, 51.4 g of ammoniumheptamolybdate tetrahydrate (Aldrich Chemical Company), 10.1 g ofammonium metavanadate (Alfa-Aesar) and 15.4 g of telluric acid (AldrichChemical Company) were dissolved upon heating to 70° C. After cooling to40° C., 267.5 g of an aqueous solution of niobium oxalate (ReferenceMetals), containing 1.25% Nb was added to the three component mixture toobtain a solution. After removing the water via a rotary evaporator witha warm water bath at 50° C. and 28 mm Hg, the solid materials werefurther dried in a vacuum oven at 25° C. overnight and then calcined.(Calcination was effected by placing the solid materials in an airatmosphere and then heating them to 275° C. at 10° C./min and holdingthem under the air atmosphere at 275° C. for one hour; the atmospherewas then changed to argon and the material was heated from 275° C. to600° C. at 2° C./min and the material was held under the argonatmosphere at 600° C. for two hours.) The catalyst thus obtained waspressed in a mold and then broken and sieved to 10-20 mesh granules forreactor evaluation.

Comparative Example 2

In a 600 mL beaker containing 223 g of water, 24.2 g of oxalic acid weredissolved and then 58.9 g of catalyst powder from Comparative Example 1were added. This mixture was heated to 75° C. and held at 75° for sixhours with stirring. After cooling this mixture to 25° C., the solidmaterials were collected by vacuum filtration and dried in a vacuumovernight. These dried materials were heated in argon to 600° C. at 2°C./min and held under argon at 600° C. for two hours. The catalyst thusobtained was pressed in a mold and then broken and sieved to 10-20 meshgranules for reactor evaluation.

Example 1

6 g of the catalyst from Comparative Example 2 were impregnated with1.72 g of samarium in 5% HNO₃ and 5.2 g water followed by drying viarotavap at 50° C. and further drying in a vacuum oven at 25° C.overnight. These dried materials were then calcined by placing the solidmaterials in an air atmosphere and then heating them to 275° C. at 10°C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for five hours. The final catalysthad a nominal composition ofMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.125)Sm_(0.0025)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10-20 meshgranules for reactor evaluation.

Example 2

6 g of the catalyst from Comparative Example 2 were impregnated with3.37 g of samarium in 5% HNO₃ and 3.5 g water followed by drying viarotavap at 50° C. and further drying in a vacuum oven at 25° C.overnight. These dried materials were then calcined by placing the solidmaterials in an air atmosphere and then heating them to 275° C. at 10°C./min and holding them under the air atmosphere at 275° C. for onehour; the atmosphere was then changed to argon and the material washeated from 275° C. to 600° C. at 2° C./min and the material was heldunder the argon atmosphere at 600° C. for five hours. The final catalysthad a nominal compositionMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.125)Sm_(0.005)O_(x). The catalyst thusobtained was pressed in a mold and then broken and sieved to 10-20 meshgranules for reactor evaluation.

Example 3

6 g of the catalyst from Comparative Example 2 were impregnated with6.85 g of samarium in 5% HNO₃ followed by drying via rotavap at 50° C.and further drying in a vacuum oven at 25° C. overnight. These driedmaterials were then calcined by placing the solid materials in an airatmosphere and then heating them to 275° C. at 10° C./min and holdingthem under the air atmosphere at 275° C. for one hour; the atmospherewas then changed to argon and the material was heated from 275° C. to600° C. at 2° C./min and the material was held under the argonatmosphere at 600° C. for five hours. The final catalyst had a nominalcomposition of Mo_(1.0)V_(0.3)Te_(0.23)Nb_(0.125)Sm_(0.01)O_(x). Thecatalyst thus obtained was pressed in a mold and then broken and sievedto 10-20 mesh granules for reactor evaluation.

Evaluation and Results

Catalysts were evaluated in a 10 cm long Pyrex tube reactor (internaldiameter: 3.9 mm). The catalyst bed (4 cm long) was positioned withglass wool at approximately mid-length in the reactor and was heatedwith an electric furnace. Mass flow controllers and meters regulated thegas flow rate. The oxidation was conducted using a feed gas stream ofpropane, steam and air, with a feed ratio of propane:steam:air of1:3:96. The reactor effluent was analyzed by an FTIR. The results (alongwith the reaction temperature and residence time) are shown in Table 1.In all cases, the propane conversion (%), acrylic acid yield (%) andselectivity to acrylic acid (%) were higher for the catalysts consistingof the promoter added to the annealed surface (Examples 3-5) whencompared to the unpromoted catalyst (Example 2) and the catalyst withoutacid treatment (Example 1).

TABLE 1 Acrylic Selectivity Reaction Residence Propane Acid to AcrylicTemperature Time Conversion Yield Acid (° C.) (sec.) (%) (%) (%) Comp.Ex. 390 3 71 13 18 1 Comp. Ex. 390 3 38 29 77 2 Ex. 1 390 3 39 38 98 Ex.2 390 3 45 41 91 Ex. 3 390 3 50 42 84

1. A process for preparing an improved catalyst, said processcomprising: (a) providing a mixed metal oxide having the empiricalformulaA_(a)V_(b)N_(c)X_(d)O_(e) wherein A is at least one element selectedfrom the group consisting of Mo and W, N is at least one elementselected from the group consisting of Te, Sb and Se, and X is at leastone element selected from the group consisting of Nb, Ta, Ti, Al, Zr,Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, Bi, B, In, Ce, As, Ge, Sn, Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er,Tm, Yb and Lu, wherein A, V, N and X are present in such amounts thatthe atomic ratio of A:V:N:X is a:b:c:d, and wherein, when a=1, b=0.01 to2, c=0.01 to 1, d=0.01 to 1 and e is dependent on the oxidation state ofthe other elements; (b) contacting said mixed metal oxide with a liquidcontact member selected from the group consisting of organic acids,alcohols, inorganic acids and hydrogen peroxide to form a contactmixture; (c) recovering insoluble material from said contact mixture;and (d) calcining said recovered insoluble material in a non-oxidizingatmosphere in the presence of a source of halogen.
 2. A catalystproduced by the process according to claim 1.